The present invention relates to an analytical method and apparatus for determining the total nitrogen and/or carbon contents in aqueous systems such as waste water.
With respect to environmental pollution problems, there has been highly sought the appearance of an analytical method and apparatus for determining rapidly and accurately the total contents of nitrogen, carbon, phosphorus, sulfur, etc. in "aqueous" systems by element, which may constitute the source of nutritional enrichment or red water in waters.
For analyzing the total nitrogen content in aqueous systems, there are known the so-called wet chemical methods, which however require an extremely long time for measurement. Further, in order to obtain accurate analytical values, sufficient knowledges on the reactions applied to the analysis and the influences to be caused by co-existing components are necessary. Furthermore, the persons who carry out the analytical methods are required to have highly technical skill. There are also proposed some analytical methods using instruments such as a method for detection of ammonia produced from hydrogenative decomposition of nitrogenous materials by coulometry, a method for the detection of chemical fluorescence on the formation of nitrogen dioxide by the reaction of nitrogen monoxide derived from nitrogenous materials with ozone and a method for detection of nitrogen monoxide produced from nitrogenous materials by the use of an infrared analyzer.
On the other hand, as to the analysis of the total carbon content in aqueous systems, there are known a method wherein carbonaceous materials are decomposed in a carrier gas containing oxygen at high temperatures and the resulting carbon dioxide is quantitatively determined (U.S. Pat. No. 3,296,435), a method wherein carbonaceous materials are decomposed in a carrier gas containing no oxygen in the presence of a catalyst such as palladium at elevated temperatures and the resulting carbon dioxide is determined quantitatively by means of an infrared analyzer (U.S. Pat. No. 3,530,292), etc. These methods are, however, disadvantageous in using an infrared analyzer, which is still expensive. Analytical methods using a gas chromatograph instead of the use of an infrared analyzer are proposed, but they are defective on the operation or the safety, because the gas produced by decomposition is stored once in a holder to make uniform and then subjected to analysis, or measurement is made by the use of a hydrogen flame ionization detector utilizing dangerous hydrogen gas.
For the simultaneous determination of the total nitrogen and carbon contents, there are proposed only few methods, of which a typical one is based on the principle of an elemental analyzer for carbon, hydrogen and nitrogen and comprises subjecting carbonaceous materials to combustion in the presence of oxygen and subjecting nitrogenous materials to reduction, followed by determination of the amounts of the resultant carbon dioxide and nitrogen using a gas chromatograph. However, this method requires a special and complicated device for the supply of oxygen gas.
A basic object of the present invention is to provide an analytical method for the determination of the total nitrogen and/or carbon contents in aqueous systems containing nitrogenous and/or carbonaceous materials. Another object of the present invention is to provide an analytical method for determining rapidly and accurately the total nitrogen and carbon contents in aqueous systems containing nitrogenous and carbonaceous materials by a simple operation. A further object of the present invention is to provide an analytical apparatus for determination of the total nitrogen and/or carbon contents in aqueous systems containing nitrogenous and/or carbonaceous materials. A still further object of the present invention is to provide an analytical apparatus for determining rapidly and accurately the total nitrogen and carbon contents in aqueous systems containing nitrogenous and carbonaceous materials which comprises readily available and less expensive instruments. These and other objects of the present invention will be apparent to those skilled in the art from the foregoing and subsequent descriptions.
The analytical method of the present invention comprises introducing an aqueous solution containing nitrogenous and/or carbonaceous materials as a specimen to be analyzed together with a carrier gas into a reactor tube packed with a destructive oxidation catalyst and/or a reducing agent and/or an oxidizing agent and maintained at certain elevated temperatures so as to decompose the nitrogenous and/or carbonaceous materials to nitrogen and/or carbon dioxide and measuring the amounts of nitrogen and/or carbon dioxide in the resulting gaseous mixture by the use of a thermal conductivity gas chromatograph.
The said analytical method may be carried out by the use of an apparatus which comprises a reactor tube provided with an inlet and an outlet through which a carrier gas is passed and packed with a destructive oxidation catalyst and/or a reducing agent and/or an oxidizing agent, a means for injecting a specimen to be analyzed into the reactor tube, a means for supplying an inert gas as the carrier gas into the reactor tube, a means for removal of moisture from the gaseous mixture produced in the reactor tube and a gas chromatograph provided with a thermal conductivity detector.
A specimen to be analyzed, which is an aqueous solution containing nitrogenous and/or carbonaceous materials, is introduced from the injector means into the reactor tube, usually through the inlet for the carrier gas.
Examples of the inert gas as the carrier gas are helium, argon, etc. Preferred is helium, because it has a larger difference from nitrogen and carbon dioxide in thermal conductivity. When the determination of the total carbon content is intended, nitrogen may be also used as the carrier gas. In case of the determination of the total nitrogen content with or without the total carbon content, however, nitrogen can not be used as the carrier gas. The inert gas from the supply means is introduced into the reactor tube, usually at a flow rate of about 20 to 200 ml/min.
The reactor tube may be made of a heat and corrosion resistant material such as quartz or ceramics (e.g. mullite). While no particular limitation exists on the size of the reactor tube, a typical example of practically utilizable reactor tubes is the one having an inner diameter of about 7 to 13 mm and an inner volume of about 20 to 50 ml.
The reactor tube is packed with a destructive oxidation catalyst and/or a reducing agent and/or an oxidizing agent. When only the determination of the total nitrogen content is intended, the reactor tube may be packed with a destructive oxidation catalyst and a reducing agent. In this case, the destructive oxidation catalyst is to be positioned on the side of the inlet and the reducing agent on the side of the outlet. When only the determination of the total carbon content is intended, the oxidizing agent alone or together with the destructive oxidation catalyst may be packed into the reactor tube. For accelerating the decomposition of carbonaceous materials and avoiding the pulverization of the oxidizing agent, it is usually preferred to use the oxidizing agent with the destructive oxidation which is positioned on the side of the inlet. In case of the determination of the total contents of nitrogen and carbon being aimed at, the destructive oxidization catalyst, the reducing agent and the oxidizing agent are packed in the reactor tube. Preferably, these materials may be arranged in the said order in the reactor tube from the inlet side to the outlet side.
The reactor tube is heated by a conventional heating means so as to maintain the zone packed with the destructive oxidation catalyst at a temperature of from about 700.degree. to 1200.degree. C (preferably from about 700.degree. to 1000.degree. C) and the zone(s) packed with the reducing agent and/or the oxidizing agent at a temperature of from about 300.degree. to 700.degree. C. When only the oxidizing agent (i.e. without the destructive oxidation catalyst and the reducing agent) is used as the packing material, it may be heated at a temperature of from about 700.degree. to 1200.degree. C.
As the destructive oxidation catalyst, there may be used the one comprising at least one metal belonging to Group IB or VIII in the periodic table. In view of the high stability at elevated temperatures, the use of a platinum group metal such as platinum or palladium is favorable. The destructive oxidation catalyst may be employed in any conventional form which does not prevent the flow of a gaseous material (e.g. pellets, wires, gauzes). When desired, the destructive oxidation catalyst may be the metal deposited on a conventional carrier material (e.g. asbestos, alumina). The destructive oxidation catalyst heated at a temperature from about 700.degree. to 1200.degree. C can decompose nitrogenous and carbonaceous materials in cooperation with the oxidizing action of water at such high temperature to produce lower molecular compounds, of which portions are further converted into nitrogen and carbon dioxide.
As the reducing agent, there may be used the one comprising at least one of copper, nickel, iron, cobalt and zinc. In view of the high reducing power, preferred are reduced copper or reduced nickel. The reducing agent may be employed in any conventional form (e.g. pellets, wires, gauzes). The reducing agent heated at a temperature of from about 300.degree. to 700.degree. C is effective in converting nitrogenous oxides present in the gaseous mixture coming through the preceding zone of the destructive oxidation catalyst into nitrogen and also in eliminating oxygen in the said gaseous mixture.
As the oxidizing agent, there may be used the one comprising at least one of oxides of cobalt, nickel, vanadium, tungsten, silver and manganese. They may be used alone or in combination. A typical example of their mixture is hopcalite, i.e. a mixture of manganese oxide, copper oxide, cobalt oxide and silver oxide. In view of the high oxidizing power at elevated temperatures, the use of oxides of cobalt is preferred. The form of the oxidizing agent may be any conventional one (e.g. pellets, wires, gauzes). The oxidizing agent heated at a temperature of from about 300.degree. to 700.degree. C accomplishes the conversion of the incompletely oxidized carbonaceous compounds present in the gaseous mixture coming through the preceding zone of the destructive oxidation catalyst to the completely oxidized carbonaceous compound, i.e. carbon dioxide.
In the reactor tube, the nitrogenous and/or carbonaceous materials are decomposed to nitrogen and/or carbon dioxide. The gaseous mixture comprising these gaseous materials flows out from the reactor tube through the outlet and is led into the means for removal of moisture. As the means for removal of water, there may be employed any conventional one such as a tube packed with a dehydrating agent (e.g. magnesium perchlorate, phosphorus pentoxide, ion exchange resin) or an electronic cooler.
Then, the gaseous mixture made moisture-free is sent to the thermal conductivity gas chromatograph for detecting nitrogen and carbon dioxide, which may be any conventional one. Both of a single column passage type and a double column passage type are utilizable. In the separation column, any conventional packing material for gas chromatography may be used, and specific examples are silica gel, activated carbon, porous polymer beads, etc.